It is common in the textile industry to apply treating material, such as, for example, dye or sizing to sheets of textile material either by transporting the sheets of textile material through a bath or baths containing treating material in liquid form, or, now more preferably, applying the treating material in a foamed form by an applicator or applicators that dispense the foam into or onto the surface or surfaces of the sheets of traveling textile substrate with the foam ultimately breaking down into liquid form. In most instances, applying the treating material in a foamed condition is preferred as it can be controlled to penetrate through the textile substrate or to be deposited only on the surface or surfaces of the textual substrate using one or a plurality of applicators. Most importantly, applying the treating material in the form of a foam has the decided advantage of generating much less wastewater that must be treated and disposed of in comparison with treating material applied in liquid form, such as in a liquid bath.
When foamed treating material under pressure is applied to nonwoven, woven, or knit textile substrate, with resisting pressure applied to the traveling substrate, the resisting pressure compresses the material of the substrate reducing the size of interstices, or spaces, which normally do not extend through the substrate, such that the foamed treating material does not significantly seep through the material being treated and creating waste water.
On the other hand, yarns in a sheet of yarns do not appreciably compress and spacing occurring from separation of yarns and yarn crossovers occurring during travel of the sheet of yarns are pronounced and extend through the sheet from one surface to the other, allowing the foam or resulting liquid to pass directly through the substrate more freely and escape from the substrate, creating increased wastewater, and passing into adjacent spaces, resulting in uneven distribution of the treating material throughout the substrate.